Solid Acid Catalyzed Hydrolysis of Cellulosic Materials

ABSTRACT

Provided are methods for the solubilization of cellulose into soluble sugars without the need for high temperatures, high pressures, strong acid solutions, and/or added water. The produced sugars can be fermented into ethanol. In one embodiment, the method comprises contacting a cellulose-containing material with a solid acid material and agitating the cellulose-containing material and the solid acid material for a time sufficient to produce an aqueous solution comprising a quantity of soluble sugars.

RELATED APPLICATIONS

This application is a continuation-in-part of PCT/US08/082,386 filedNov. 5, 2008, which claims priority to U.S. Ser. No. 11/935,712 filedNov. 6, 2007, which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to processes for the hydrolysis ofcellulose-containing material, and more particularly to processes forthe hydrolysis of cellulose-containing material into soluble sugarsusing a solid acid material.

BACKGROUND OF THE INVENTION

Ethanol is the most widely used liquid biofuel in the world. In theU.S., ethanol is typically used as a gasoline additive and is blendedinto gasoline at up to 10 percent by volume to produce a fuel called E10or “gasohol.” In 2005, total U.S. ethanol production alone was 3.9billion gallons, or 2.9 percent of the total gasoline pool. In 2006,that number increased to 4.86 billion gallons, and is well on pace tofurther rise in 2007. Therefore, the efficient and inexpensiveproduction of materials to produce ethanol is of great interest.

One source of feedstock material to produce ethanol is soluble sugarsproduced by hydrolyzing cellulose. Such hydrolysis processes currentlydraw significant interest because large amounts of cellulosicfeedstocks, such as biomass materials, can be easily and cheaplyobtained, and environmentally, the burning or landfilling of wastecellulosic materials can be reduced. Exemplary types of biomassmaterials include switchgrass, wood, paper, agricultural residues,industrial solid wastes, and herbaceous crops. The hydrolysis processesare characterized by the breaking of the bonds between the glucosemonomer units of cellulose to provide soluble sugar moieties, which arefermentable into ethanol.

Two hydrolysis methods are commonly used: acid hydrolysis and enzymatichydrolysis. However, neither process is optimal. Acid hydrolysis can beperformed with dilute or concentrated acid. Unfortunately, dilute acidsrequire high temperature and pressures while concentrated acids must beremoved from the product before fermentation can occur. On the otherhand, enzymatic processes require a stable supply of enzymes andpretreatment to more easily hydrolyze the cellulose, especially withlignocellulosic material. Also, as set forth in U.S. Pat. Nos. 6,419,788and 4,461,648, for example, because of the complex chemical structure oflignocellulosic material, which includes lignin and hemicellulose thatcoat the cellulose, microorganisms and enzymes cannot effectively attackthe cellulose without prior treatment because the cellulose is highlyinaccessible to enzymes or bacteria. Accordingly, there is a need for amore efficient and inexpensive method of producing fermentable sugarsfor the mass production of ethanol.

SUMMARY OF THE INVENTION

The inventors have unexpectedly found that when a solid acid material iscombined with a cellulose-containing material and agitated, a high yieldof soluble sugars can be produced. In the process, the agitation of thematerial, typically in a mill, provides the kinetic energy necessary todrive the hydrolysis reaction while the solid acid material has asurface acidity that aids in hydrolyzing the glycosidic bonds of thecellulose material. In addition, when the solid acid material has asufficient existing water content, the water of the solid acid materialcan provide the water necessary for the hydrolysis reaction without theneed for added water. For example, in one embodiment of the presentinvention, the solid acid material is a material, such as kaolin orbentonite, which has a surface acidity as well as a water content. Theresulting products of the hydrolysis reaction, which include a quantityof soluble and fermentable sugars, are useful in the production ofethanol and for other purposes.

Moreover, the inventors have found that when the cellulose-containingmaterial is a lignocellulosic material, the solid acid material may alsohydrolyze the hemicellulose and lignin of the lignocellulosic material.Hemicelluloses are non-cellulosic polysaccharides that are built upmainly of sugars other than glucose, i.e. D-xylose with other pentosesand some hexoses with β-linkages. They are generally poorly ordered andnon-crystalline and have a much lower chain length than cellulose.Lignin is an aromatic polymer, phenolic in nature, and built up fromphenylpropane units, but with no systematic structure. Thus, when thecellulose-containing material is a lignocellulosic material, thehemicellulose and lignin of the material can also be decomposed intouseful products, namely further soluble sugars and aromatichydrocarbons, such as vanillin, respectively. In this way, the presentinvention can eliminate waste from the hydrolysis of lignocellulosicmaterial, as well as eliminate the need to pre-treat the cellulosematerial before hydrolyzing the lignocellulosic material, as in knownprocesses.

In view of the above, in accordance with one aspect of the presentinvention, there is provided a method for the production of solublesugars from a cellulose-containing material, comprising: (a) contactingthe cellulose-containing material with a solid acid material; and (b)agitating the cellulose-containing material and the solid acid materialfor a time sufficient to produce a product comprising soluble sugars.Optionally, an initial aqueous solution may be recovered after the stepof agitating that comprises soluble sugars. The cellulose-containingmaterial may be a pure cellulose material or any other type ofcellulose-containing material, such as a biomass or lignocellulosicmaterial. The solid acid material may be any type of solid or semi-solidmaterial having a surface acidity, defined as H₀, with a value of lessthan about −3.0, and more preferably less than about −5.6.

Optionally, the method further comprises: (c) after the step ofagitating, recovering a second aqueous solution comprising solublesugars by rinsing the solid acid material and the cellulose-containingmaterial with an aqueous solution. In addition, since the solid acidmaterial is not a reactant in the hydrolysis process, after the step ofrecovering, the process optionally further comprises: (d) reusing aquantity of solid acid material and repeating steps (a) and (b), andoptionally (c) above, with further cellulose-containing material. Theprocess may be performed within a mill or any other suitable vessel thatprovides agitation of the material therein.

In accordance with another aspect of the present invention, there isprovided a method for the production of soluble and fermentable sugarsfrom a cellulose-containing material, comprising:

(a) contacting the cellulose-containing material with a solid acidmaterial; and

(b) agitating the cellulose-containing material and the solid acidmaterial for a time sufficient to produce a product comprising solublesugars, wherein agitating occurs at a temperature of between about −5 toabout 105 degrees Celsius, and wherein said cellulose-containingmaterial and solid acid material have a combined free water content ofabout 45% or less. Thereafter, the method optionally includes steps (c)and (d) as described above.

Thus, the present invention also contemplates that certain types ofsolid acid materials may inherently have a water content that enablesthe hydrolysis of the cellulose-containing material to occur without theneed for added water. This water may be present as water ofcrystallization of the solid acid material or materials therein, or asabsorbed or adsorbed water of the solid acid material (referred to asthe “free water content” below). At least a portion of the water ofcrystallization may be removed during the steps of agitating asdescribed herein. Moreover, water necessary for the hydrolysis of thecellulose may be provided by any moisture or water contained in thecellulose-containing material. In addition, in the hydrolysis ofcellulose, a dehydration of glucose may take place to provide furtherwater for the hydrolysis reaction.

In accordance with another aspect of the present invention, during thestep (b) of agitating, the free water content of the solid acid materialis in the range of about 4% to about 10% by weight of the solid acidmaterial. The free water content of the cellulose-containing materialand the solid acid material is collectively less than about 45% byweight, and preferably from about 8% to about 40% by weight, so as tonot undesirably lower the kinetic energy needed for the hydrolysisreaction upon agitating. By “free water content,” it is meant an amountof water in the cellulose-containing material and solid acid containingmaterial that is contained within the cellulose-containing material andthe solid acid material, but does not pertain to a water of hydration orcrystallization of either material. In this way, there is sufficientwater in the mixture to drive the hydrolysis reaction.

In accordance with yet another aspect of the present invention, thesolid acid material is an aluminosilicate material, such as a claymaterial. The clay material may be any one of kaolin, bentonite,fuller's earth, or an acid-treated clay material, such as acid-treatedbentonite treated with about 1 M hydrochloric acid. When the solid acidmaterial is a clay material, the clay material may have a water contentthat is attributable to a water of crystallization of the material ormaterials therein. The water of crystallization may be removed duringagitating to further provide needed water for the hydrolysis reaction.

In accordance with still another aspect of the present invention, thesolid acid material is a solid superacid material. Superacids may bedefined as acids stronger than 100% sulfuric acid (also known asBrönsted superacids). In addition, superacids may be described as acidsthat are stronger than anhydrous aluminum trichloride (also known asLewis superacids). Solid superacids are composed of solid media that aretreated with either Brönsted or Lewis acids. In one embodiment, thesolid acid is a solid superacid comprising alumina treated with 2 Msulfuric acid, filtered and calcined at about 800° C. for about 5 hours.

In accordance with another aspect of the present invention, the ratio ofthe cellulosic-containing material to the solid acid material is fromabout 0.5:1 to about 10:1. When the solid acid material is a claymaterial, in one embodiment, the ratio of the cellulosic material to thesolid acid material may be provided in the range of from about 1:1 toabout 3:1 because the clay material contains a free water content, aswell as water of crystallization.

In accordance with another aspect of the present invention, thecellulose-containing material is a lignocellulosic material. As a resultof the steps (a) and (b) of contacting and agitating in any embodimentdescribed herein, the hemicellulose is hydrolyzed into a quantity ofsoluble sugars and the lignin is decomposed into useful aromatichydrocarbons, such as vanillin. The soluble sugars from the hydrolysisof hemicellulose and the produced aromatic hydrocarbons may be recoveredin a first aqueous solution after the step of agitating from thecellulose-containing material and the solid acid material. This firstaqueous solution may also comprise soluble sugars from the hydrolysis ofcellulose. In addition, the solid acid material and the lignocellulosicmaterial may be rinsed with an aqueous solution to produce a secondaqueous solution comprising soluble sugars, as well as the aromatichydrocarbons. Thereafter, the solid acid material may be reused tohydrolyze further lignocellulosic material when combined with additionalcellulose-containing material.

Polysaccharides are polymeric carbohydrate structures formed ofrepeating units (either mono- or di-saccharides) joined together byglycosidic bonds. Cellulose is a polysaccharides that has a generalformula of (C₆H₁₂O₅)_(n) where n is typically 40-3000. When traditionalacid hydrolysis is used for production of fermentable sugars fromcellulose containing materials, the resulting polysaccharide oligomersrange from n=1 to n=7. The inventors have found that mechnocatalyticacid hydrolysis according to the methods taught herein consistentlyproduces a polysaccharide oligomer material wherein the materialcontains at least a majority of polysaccharide oligomers having an n nogreater than n=2. In a more specific embodiment, the polysaccharideoligomer content of the product of hydrolyzing the cellulose-containingmaterial comprises 70 percent or more oligomers having a n no greaterthan 2. In an even more specific embodiment the polysaccharide oligomercontent comprises at least 80 percent, at least 85 percent, at least 90percent, at least 95 percent or 100 percent of oligomers having an n nogreater than n=2. Thus, based on this, and in view of the teachingsherein, those skilled in the art will be enabled to identify ahydrolyzed product produced according to embodiments of the presentinvention. Furthermore, the ability to breakdown cellulose intopolysaccharide oligomers of such a small size provides a materialcomprising a higher yield of fermentable sugars. This, of course,equates to higher efficiencies and lower cost for producing ethanol andother products from cellulose.

According to other certain method embodiments, the hydrolyzed productpossesses a specific sugar profile. Thus, according to one embodiment,the invention pertains to a hydrolyzed product (typically in the form ofa liquid suspension) of hydrolysis of a cellulose-containing materialcomprising 3 or more of the following: cellobiose, glucose, fructoselevoglucosan levoglucosenone, furfural, and 5-hydroxymethylfurural. Inanother embodiment, the hydrolyzed product comprises levoglucosenoneand/or furfural. In an even more specific embodiment, the hydrolyzedproduct comprises levoglucosenone and furfural. The inventors havedetermined that such components are not produced by the conventionaltechniques of acid hydrolysis or enzymatic hydrolysis ofcellulose-containing materials. Accordingly, based on this, and in viewof the teachings herein, those skilled in the art will be enabled toidentify a hydrolyzed product produced according to embodiments of thepresent invention.

Upon hydrolysis according to certain embodiments of the invention, theresultant product is then either directly subjected to fermentation(according to convention techniques) or is subjected to an intermediateenzymatic hydrolysis step.

These and other advantages will be apparent from the disclosure of theinvention(s) contained herein.

As used herein, “at least one”, “one or more”, and “and/or” areopen-ended expressions that are both conjunctive and disjunctive inoperation. For example, each of the expressions “at least one of A, Band C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “oneor more of A, B, or C” and “A, B, and/or C” means A alone, B alone, Calone, A and B together, A and C together, B and C together, or A, B andC together.

The above-described embodiments and configurations are neither completenor exhaustive. As will be appreciated, other embodiments of theinvention are possible utilizing, alone or in combination, one or moreof the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of thedrawings that show:

FIG. 1 is a flow schematic of one embodiment of the present invention;

FIG. 2 shows the solubilization efficiency of various solids after threehours of milling in accordance with the present invention;

FIG. 3 shows the effect of milling time on the solubilization ofcellulose.

FIG. 4 shows the water content of bentonite through the mass loss ofbentonite by heating the bentonite material;

FIG. 5 shows the mass loss of cellulose upon heating indicating anadsorbed moisture content of about 4% by weight;

FIG. 6 shows the optimal ratio of cellulose to kaolinite forsolubilizing cellulose; and

FIG. 7 shows the optimal ratio of cellulose to bentonite forsolubilizing cellulose; and

FIG. 8 shows the progression of the solubilization of cellulose and thesoluble sugars produced over time on a thin-layer chromatography plateduring a process in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Now referring to the figures, FIG. 1 shows a schematic representation ofa process 100 for the production of soluble and fermentable sugars froma cellulose-containing material in accordance with one aspect of thepresent invention. In step 102, a quantity of a cellulose-containingmaterial is contacted with a quantity of a solid acid material. Toaccomplish this, the materials may be introduced into any suitablevessel, and preferably the vessel in which the step of agitating willtake place, by any suitable method, and simultaneously or sequentiallyone after the other. While not necessary, it is contemplated that thecellulose-containing material may be pretreated as desired, such as bybreaking or grinding the material down to a desired size, beforebringing the cellulose-containing material and solid acid material intocontact with one another.

The cellulose-containing material may be any material or mixture ofmaterials having a cellulose content. Thus, in one embodiment, thecellulose-containing material may be a purified source of cellulose. Inanother embodiment, the cellulose-material is a natural cellulosicfeedstock, typically referred to as a “biomass.” Exemplary biomassmaterials include wood, paper, switchgrass, wheat straw, agriculturalplants, trees, agricultural residues, herbaceous crops, starches, cornstover, saw dust, and high cellulose municipal and industrial solidwastes.

In one embodiment, the biomass material is a lignocellulosic materialhaving a cellulose, hemicellulose, and lignin content. Typically, insuch lignocellulosic material, the cellulose, hemicellulose, and ligninare bound together in a complex gel structure along with smallquantities of extractives, pectins, protein, and ash. As discussedabove, generally, lignocellulosic material is poorly accessible tomicroorganisms, yeast, and enzymes, and the like that are sometimes usedto hydrolyze cellulose. A substantial benefit of the present inventionis that when the cellulose-containing material is a lignocellulosicmaterial, the lignin and hemicellulose can also be broken down intouseful products by the solid acid material of the present invention,thereby eliminating waste from the process and eliminating the need topurify the cellulose material before hydrolyzing the material. Anyquantity of cellulose-containing material may be provided in the presentinvention in the ratios set forth herein.

The solid acid material may be any solid material having a surfaceacidity. By “solid,” it is meant a solid material, a semi-solidmaterial, or any other material having a water content of less thanabout 40% by weight. Surface acidity refers to the acidity of the solidsurface of the material. Surface acidity determination methods arefounded on the adsorption of a base from the base's solution. The amountof base that will cover the solid surface of the solid acid materialwith a monolayer is defined as the surface acidity and corresponds tothe pK_(a) of the based used. The base used may be n-butylamine,cyclohexamine, or any other suitable base. The degree of surface acidityis typically expressed by the Hammet and Deyrups H₀ function.

H ₀ =pK _(BH+)−log(C _(BH+) /C _(B))  (I)

Thus, in this equation, when an indicator, B, is adsorbed on an acidsite of the solid surface of the material, a part of the indicator isprotonated on the acid site. The strength of the acid sites may berepresented by Formula (I) by the value of pK_(BH+) of BH⁺. BH⁺ is theconjugate acid of indicator B when the concentration of BH⁺(C_(BH+)) isequal to the concentration of B (C_(B)). Therefore, the acid strengthindicated by H₀ shows the ability of the conjugate to change into theconjugate acid by the acid sites that protonates half of the baseindicator B. Under a Lewis definition, the H₀ value shows the abilitythat the electron pair can be received from half of the absorbed baseindicator B. See Masuda et al., Powder Technology Handbook, 3^(rd) Ed.(2006). A H₀ of −8.2 corresponds to an acidity of 90% sulfuric acid anda H₀ of −3.0 corresponds to an acidity of about 48% sulfuric acid.

Any suitable method of determining the H₀ of a material may be used,such as the method using the adsorption of n-butylamine from itssolution in cyclohexane as set forth in Investigation of the SurfaceAcidity of a Bentonite modified by Acid Activation and ThermalTreatment, Turk. J. Chem., 2003; 27:675-681, the disclosure of which ishereby incorporated by reference in its entirety. Alternatively,indicators, generally referred to as Hammett indicators, may be used todetermine the H₀ of a material. Hammett indicators rely on color changesthat represent a particular surface acidity of the subject material.

In the present invention, a number of solid acid materials may be used.Generally, the solid acid material in the present invention may be anysolid material having a surface acidity. Preferably, the solid acidmaterial has an H₀ of less than about −3.0, and preferably less thanabout −5.6.

In one embodiment, the solid acid material is a clay material. As usedherein, “a clay material” is defined as a material composed primarily offine-grained minerals, which is generally plastic at appropriate watercontents and will harden with dried or fired. Exemplary minerals thatcomprise the major proportion of clay materials for use in the presentinvention include kaolinite, halloysite, attapulgite, montmoirllonite,illite, nacrite, dickite, and anauxite. Non-limiting examples of claysfor use in the present invention include fuller's earth, kaolin, andbentonite. Kaolin is a clay material that mainly consists of the mineralkaolinite. Bentonite is a clay containing appreciable amounts ofmontmorillonite, and typically having some magnesium and associatedtherewith. Optionally, the clay material may be acid-treated to providefurther surface acidity to the clay material.

In another embodiment, the solid acid material is any aluminosilicate orhydrated aluminosilicate mineral. For example, the solid acid may bevermiculite, muscovite mica, kaolinite, halloysite, attapulgite,montmorillonite, illite, nacrite, dickite, and anauxite, or zeolitessuch as analcime, chabazite, heulandite, natrolite, phillipsite, andstilbite, or any mineral having the general formula Al₂O₃.xSiO₂.nH₂O.

In another embodiment, the solid acid material is a superacid material.Superacid materials are useful in the present invention because of thehigh number of acidic sites on the surface of the superacid material.Brönsted superacids may be described as acids which are stronger than100% sulfuric acid. Lewis superacids may be described as acids that arestronger than anhydrous aluminum trichloride. Solid superacids arecomposed of solid media, i.e. alumina, treated with either Brönsted orLewis acids. The solids used may include natural clays and minerals,metal oxides and sulfides, metal salts, and mixed metal oxides.Exemplary Brönsted superacids include titanium dioxide:sulfuric acid(TiO₂:H₂SO₄) and zirconium dioxide:sulfuric acid (ZrO₂:H₂SO₄) mixtures.Exemplary Lewis superacids involve the incorporation of antimonypentafluoride into metal oxides, such as silicon dioxide (SbF₅:SiO₂),aluminum oxide (SbF₅:Al₂O₃), or titanium dioxide (SbF₅:TiO₂). In oneembodiment, the superacid is a metal oxide treated with treated witheither Brönsted or Lewis acids. In a particular embodiment, thesuperacid is alumina treated with sulfuric acid as set forth below.

Alternatively, the solid acid material may be a silicate material, suchas talc or any other suitable solid material having a surface acidity,such as alumina, and combinations of any of the materials describedherein.

As shown in FIG. 2, the solubilization efficiency for a number ofmaterials was compared for the solubilization of cellulose after threehours of milling in a SPEX 8000D mixer mill available from SPEXCertiPrep of Metuchen, N.J. The materials that provided the best resultswere those material having a surface acidity value (H₀) of less thanabout −3.0. Acidified bentonite, kaolin, anhydrous kaolinite, a superacid in the form of aluminum oxide treated with sulfuric acid, all haveH₀ values of less than about −3.0. Acidified bentonite and kaolinprovided the best solubilization efficiencies, followed by anhydrouskaolinite, a super acid in the form of aluminum oxide treated withsulfuric acid, bentonite, alumina, vermiculite, muscovite mica, talc,silicon carbide, graphite, aluminum sulfate, and rice hull ash. Siliconcarbide, graphite, aluminum sulfate, and rice hull ash are known not tohave any appreciable surface acidity.

Since kaolin provided a high degree of solublization, specifically, asolublization efficiency for cellulose of at least about 70%, in oneembodiment, the solid acid material is kaolin. Kaolin is composedprimarily of the mineral kaolinite. Kaolinite (Al₂Si₂O₅(OH)₄) is alayered silicate made of alternating sheets of octahedrally coordinatedaluminum and tetrahedrally coordinated silicon that are bonded byhydroxyl groups. Alternatively, the solid acid may be in the form ofanhydrous kaolin, which may be prepared by heating kaolin at about 800°C. for at least about 6 hours and preferably at about 800° C. for about8 hours.

In another embodiment, the solid acid is bentonite, and preferablyacidified bentonite. Bentonite is an absorbent aluminum phyllosilicategenerally impure clay consisting mostly of montmorillonite,(Na,Ca)_(0.33)(Al,Mg)₂Si₄O₁₀(OH)₂.(H₂O)_(n). Two types exist: swellingbentonite which is also called sodium bentonite and non-swellingbentonite or calcium bentonite. Preferably, the bentonite isnon-swelling bentonite. The acidified bentonite may be prepared bytreating bentonite with one or more acids, such as by treating bentonitewith 1 M hydrochloric acid solution.

In still another particular embodiment, the solid acid is a solidsuperacid comprising alumina treated with 2 M sulfuric acid, filteredand calcined at about 800° C. for about 5 hours.

Kaolin and acidified bentonite are desirable materials for use in thepresent invention because they provide a high surface acidity along withan inherent an amount of water, both due to a water of crystallizationand a free water content, which are both useful to hydrolyze theglycosidic bonds of the cellulose material. Therefore, using acidifiedbentonite, bentonite, and kaolin as the solid acid material can providea substantial benefit as the use of the materials may eliminate the needfor added water to the solubilization process, thereby significantlydecreasing time and expense in the solubilization of cellulose.

Accordingly, in one embodiment, the free water content of the solid acidmaterial is from about 4% to about 10% by weight. Kaolin and bentonitegenerally have a free water content of greater than about 4% by weight,as well as a water of crystallization content. Water of crystallizationrefers to water that occurs as a constituent of crystalline substancesin a definite stoichiometric ratio. This water can be removed from thesubstances by the application of heat at about 700° C. and its lossusually results in a change in the crystalline structure. In the presentinvention, it is believed that the agitating step as described hereinprovides the localized heat necessary to remove the water, includingwater of crystallization, from the solid acid material (when water ofcrystallization is present) to provide further water for the hydrolysisof the cellulose-containing material.

The water content of most compounds, including the water ofcrystallization of the subject material, can be determined bythermogravimetric analysis (TGA), where the sample is heated, and theaccurate weight of a sample is plotted against the temperature.Alternatively, any other suitable method for determining water contentmay be used, including mass loss on heating, Karl Fischer filtration,and freeze drying, or any other suitable method.

As shown in FIG. 4, heating 5 milligrams of bentonite to a temperatureof 850° C. at a rate of 10° C./minute showed a water loss of from about7.0 to about 7.5% by mass at 100° C. for adsorbed water and anadditional mass loss of another about 5% to about 6% by mass due to thewater of crystallization. It is believed that kaolin has a similar freewater content relative to bentonite. As discussed above, the water ofcrystallization and the free water content of the clay materials areuseful for the hydrolysis of the cellulosic glycosidic bond in theprocesses of the present invention.

In another embodiment, the solid acid material is an acid-treatedmaterial, such as sulfuric acid-treated alumina to form a superacid. Toprepare this superacid, alumina was stirred in 2 M sulfuric acid,filtered and calcined at about 800° C. for about 5 hours. Treating thealumina with sulfuric acid adds sulfate ions to the solid aluminasurface, thereby allowing the solid acid material to further acceptelectrons. As a result, these superacids have a very high surfaceacidity. However, while superacids may have a higher surface aciditythan bentonite or kaolinite, the superacids may not have as much waterpresent. As a result, while not wishing to be bound by theory, itappears the additional water content found in kaolin and bentonitecontributes to the higher solubilization efficiency for cellulose foundwith bentonite or kaolonite over acid-treated alumina. This statement isfurther supported in showing that the solubilization efficiency is lowerfor anhydrous kaolinite vs. kaolin, which has a higher water content.

The ratio of the cellulose-containing material to the solid acidmaterial is such that the solubilization of cellulose is optimized.Generally, the solubilization efficiency is optimized by determining aratio of the cellulose-containing material to the solid acid material,wherein a surface interaction of the solid acid and cellulose-containingmaterial is maximized and the combined water content of the cellulosematerial and solid acid material is optimized. If there is too muchmoisture in the combined cellulose-containing material and the solidacid material, or the individual materials during agitating of thematerials, the amount of kinetic energy available to drive thehydrolysis of cellulose is lowered and the process results in a loweredyield of soluble and fermentable sugars. On the other hand, incompletesolubilization of the cellulose-containing material results if the watercontent is too low.

In one embodiment, the cellulose-containing material is provided in aratio of from about 0.5:1 to about 10:1 cellulose-containing material tosolid acid material. In a particular embodiment, when the solid acidmaterial is kaolin, FIG. 6 shows that the optimal yield of soluble andfermentable sugars is obtained with about an 1:1 mass ratio of celluloseto kaolin after about 2 hours of milling in a SPEX 8000D shaker millavailable from SPEX CertiPrep of Metuchen, N.J. The material was milledin 0.5 hour increments in 50 mL milling vials constructed of 440Cstainless steel with 3 440C steel balls ½″ diameter as the millingmedia. Similarly, FIG. 7 shows that the optimal yield of soluble andfermentable sugars is obtained with a 1:2 mass ratio of cellulose tobentonite after two hours of milling in a SPEX 8000D shaker mill. Thematerial was milled in 0.5 hour increments in 50 mL milling vialsconstructed of 440C stainless steel with 3 440C steel balls ½″ diameteras the milling media.

In one embodiment, the cellulose-containing material has a free watercontent of from about 4% to about 40% of the cellulose-containingmaterial. As shown in FIG. 5, by heating 3.5 milligrams of 100% purecellulose (Avicell microcrystalline cellulose, obtained from FisherScientific) to a temperature of about 850° C. at a rate of about 10°C./min. The mass loss at about 100° C. indicated an adsorbed moisturecontent of about 4%.

From calculations, it is known that to convert 100% cellulose to 100%fructose or glucose, the minimum water required is 4.76% by weight.Thus, when the cellulose-containing material and the solid acid arecontacted in step 102, in one embodiment, the free water content of thecollective mixture is less than about 45% by weight of the materials,and more preferably from about 8% to about 40% by weight of thematerials. In this way, a sufficient water content is provided to drivethe hydrolysis of cellulose at ambient temperature and without therequirement of added water. This may result in huge savings to oneperforming the processes described herein on a large, manufacturingscale. Optionally, however, water may added as needed at any of thesteps of the processes described herein to provide the necessary watercontent to drive the hydrolysis reaction.

In step 104, the cellulose-containing material and the solid acidmaterial are agitated for a time sufficient to provide a productcomprising a quantity of soluble sugars. The agitation may take place inany suitable vessel or reactor. In one embodiment, the agitating takesplace in a ball, roller, jar, hammer, or shaker mill. The millsgenerally grind samples by placing them in a housing along with one ormore grinding elements and imparting motion to the housing. The housingis typically usually cylindrical and the grinding elements are typicallysteel balls, but may be rods, cylinders, or other shapes. Generally, thecontainers and grinding elements are made from the same material.

As the container is rolled, swung, vibrated, or shaken, the inertia ofthe grinding elements causes the grinding elements to move independentlyinto each other and against the container wall, grinding the sample. Inone embodiment, the mill is a shaker mill using steel balls and shakingto agitate the cellulose-containing material and the solid acidmaterial. The mills for use in the present invention may range fromthose having a sample capacity of a gram or less to large industrialmills with a throughput of tons per minute. Such mills are availablefrom SPEX CertiPrep of Metuchen, N.J., for example Paul O. Abbe,Bensenville, Ill., or Union Process Inc., Akron, Ohio. For some mills,such as a steel ball mill from Paul O. Abbe, the optimal fill volume isabout 25% of the total volume of the mill. The number of steel ballsrequired for the process is dependant upon the amount of kinetic energyavailable. High energy milling like that in a shaker mill require lessballs than lower energy milling methods such as rolling mills. Forshaking mills, a ball to sample mass ratio of about 12:1 is sufficient.For rolling mills, a ball to sample mass ratio of about 50:1 works wellfor a rolling rate of about 100 rpm. Lower mass ratios can be obtainedby increasing the amount of kinetic energy available to the system. In aroller mill, this can be achieved through optimization of mill geometryand/or increasing the mill's rotational velocity.

A significant advantage of the present invention is that the processesdescribed herein can be performed at ambient temperature without theneed for added heat, cooling, or modifying pressure. Instead, theprocesses, including the agitation step, can be performed under ambientconditions. Without wishing to be bound by theory, it is believed theagitating of the cellulose-containing material with the solid acidmaterial, such as in with the aforementioned mills, provides the processwith the energy required for the hydrolysis of the cellulose, andcellulose, hemicellulose and lignin if the cellulose-containing materialis a lignocellulosic material. Moreover, it is believed the agitatingalso allows more of the cellulose-containing material to contact theacidic sites on the surface of the solid acid material. Even further, itis believed that the heat created by the agitating frees up the inherentwater content of the material contained as water of crystallization ofthe material to provide water fro the hydrolysis reaction. In analternate embodiment, the agitating may occur at a controlledtemperature of between about −5 to about 105 degrees C. It iscontemplated that agitation may occur at any temperature degree valuewithin this range (rounded to the nearest 0.5 centigrade unit), orwithin any sub-ranges within this range (rounded to the nearest 0.5centigrade unit).

After the step of agitating 104, a first aqueous solution is optionallyremoved from the vessel where the agitating is performed in recoveringstep 108 as shown. Typically, this aqueous solution will comprise anaqueous solution of soluble sugars, typically in the form ofmonosaccharides, disaccharides, and polysaccharides. When thecellulose-containing material is a lignocellulosic material, thisaqueous solution may also comprise further soluble sugars, as well asuseful aromatic hydrocarbons, such as vanillin. Vanillin is a knownflavoring additive in the food industry. It is contemplated that thefirst aqueous solution may also comprise other byproducts of thedecompositions reaction which occur, such as hydroxymethylfurfural orHMF. Hydroxymethylfurfural is an aldehydic compound that is found in anumber of foods, such as milk, fruit juices, spirits, and honey. Thus,in one embodiment, the processes as described herein can also be usedfor the production of furfurals, namely HMF, and also vanillin. Forexample, glucose produced by the hydrolysis of cellulose can be used asa starting material to produce furfurals by dehydration of the glucosecompounds. The production of HMF may be enhanced by the use of solidacids that incorporate transition metals such as, but not limited tochromium and molybdenum.

Preferably, after the step of agitating 104, the cellulose-containingmaterial and solid acid material are rinsed with an aqueous solution asset forth below in step 106. Alternatively, from recovering step 108, atleast a portion of the first aqueous solution is optionally directed toa separating step 110 as indicated by arrow 112, where any separation ofthe components of the first aqueous solution can be performed by anysuitable technique known in the art. For example, if vanillin is desiredto be separated out from the solution, the vanillin can be removed byany suitable method, such as by chromatographic methods well known inthe art. Further alternatively, at least a portion of the first aqueoussolution may be directed to fermenting step 116 as described below andindicated by arrow 114.

When using a mill as described herein, the hydrolysis processesdescribed herein are generally carried out as a batch process. Inaddition, the vessel where the agitating and hydrolysis reaction takesplace may be performed in a continuous attritter, which is commerciallyavailable from Union Process, Akron, Ohio. This device more generallyallows the process to be carried out as a continuous process.

A significant advantage of the present invention is that the vesselwhere the agitation takes place will generally provide the necessaryheat and kinetic energy to drive the hydrolysis reaction. As such, it isgenerally not necessary to add any heat to the processes as describedherein and the agitating may take place at ambient temperature. Asdescribed above, however, in an alternate embodiment, the agitating mayoccur at a controlled temperature of between about −5 to about 105degrees C. The agitating step 104 also ensures that the acidic sites onthe surface of the solid acid material interact with thecellulose-containing material in order to promote decomposition of thecellulose, and hemicellulose and lignin, if present. When the materialis a clay material or other material having a water of crystallization,the agitating may free up water for use in the hydrolysis reaction.

The milling time can have an effect on the extent of solubilization ofthe cellulose material. For example, as shown in FIG. 3, kaolinapproaches a maximum percent of solubilization after about two hours ofshaker milling in a sealed hardened steel vial with a ball to samplemass ratio of 12:1. Other materials may not have reached their maximumafter three hours of milling, the bulk of which may be fermentable intoethanol. As is also shown in FIG. 3, sulfuric acid-treated alumina,bentonite, alumina, and talc had not yet reached a maximum after threehours of shaker milling in a sealed hardened steel vial with a ball tosample mass ratio of 12:1.

As shown in FIG. 8, 1 gram of cellulose and 1 gram of kaolin were milledin hardened steel vials with 0.5″ steel balls and a ball to sample massratio of 12:1. The agitation was supplied by a SPEX 8000D mixer millavailable from SPEX CertiPrep of Metuchen, N.J. The production ofsoluble sugars was monitored over a time period of 4.5 hours bythin-layer chromatography using an EMD Chemicals cellulose TLC plate, 20cm×10 cm. A developing solution was used that consisted of a mixture ofbutanol, water, and acetic acid. The oligosaccharides were stained byspraying with a urea-phosphoric acid solution and heating to about 80°C. for about 10 minutes. This stain colors ketoses blue and aldoses apale red. Individual samples were prepared by milling samples with atotal mass of 2 grams for the prescribed amount of time in ½ hourincrements.

As can be seen by FIG. 8, a notable amount of fructose is increasinglyformed during the reaction, in addition to glucose. In addition, theagitating step 104 may produce a further quantity of soluble sugars,including sugars in the form of monosaccharides, disaccharides andpolysaccharides. For example, the solubilized sugars may bepolysaccharides up to eight glucose units. In addition, other byproductsmay be formed in the agitating step 104, such as furfurals from thedehydration of glucose and small quantities of ethanol. If ethanol isformed, the ethanol may be removed from the mill by any suitable method,such as by vacuum distillation, as the ethanol is formed. If thecellulose-containing material is a hemicellulose material, the agitatingstep 104 may also produce further soluble sugars or long-chain sugars,as well as aromatic hydrocarbons and furfurals, such as HMF. Themajority of soluble sugars produced by the processes described hereinare suitable for use in fermenting processes to produce ethanol.

It is contemplated that at least about 80% of the cellulose in thecellulose-containing material may be solubilized in embodiments of thepresent invention. It is appreciated that higher efficiencies may beobtained by selecting the various solid acids, milling time, andmodifying the ratio of the cellulose-containing material to the solidacid material. If relatively pure cellulose is used, it is contemplatedthat less cellulose-containing material may be required than if thecellulose-containing material were a biomass material, such aslignocellulose.

Referring again to FIG. 1, after step 104 of agitating, thecellulose-containing material and solid acid material may be washed withan aqueous solution in step 106 to produce a second aqueous solutioncontaining soluble sugars. The sugars may in the form ofmonosaccharides, disaccharides and polysaccharides. Any suitable methodof determining the amount of solubilized sugars may be used, such as bychromatographic methods well known in the art. Moreover, the presence ofparticular solubilized sugars may be confirmed by any suitablechromatography method, such as thin-layer chromatograph, gaschromatography (GC), high-pressure liquid chromatography (HPLC), GC-MS,LC-MS, or any other suitable method known in the art. The second aqueoussolution may also comprise furfurals, ethanol, aromatic hydrocarbons,such as vanillin as previously described herein.

The washing step 106 may be repeated until it is relatively certain thatthe bulk of the soluble sugars have been recovered in the second aqueoussolution. Thereafter, the second aqueous solution may be directed tofermenting step 116 as indicated by arrow 118 or alternatively toseparating step 110 for separation of any of the desired components byany suitable technique known in the art.

Since the solid acid is acting as a catalyst in the hydrolysis of thecellulose-containing material, the solid acid material may be recycled.Thus, optionally, the solid acid material may be directed to drying step122 to dry the material a suitable moisture content, if necessary, asshown by arrow 120 and a new quantity of cellulose-containing materialcan be combined with the all or a portion of the recycled solid acidmaterial to again produce a quantity of solubilized sugars. If no dryingstep is necessary, the rinsed solid acid material can be immediatelyreused in contacting step 102. In either instance, the rinsed solid acidmaterial is optionally recycled and reused to hydrolyze furthercellulose-containing material by starting the process again at step 102.Additional solid acid material may be added as needed to supplement therecycled solid acid material when redoing step 102. Accordingly, asignificant advantage of the present invention is that at least aportion of the solid acid material may be reused continuously, therebysavings considered material and expense.

The recovered fermentable sugars from step 108, any portion of the firstand/or second aqueous solutions, or all of the first and/or secondaqueous solutions having the soluble, and mainly fermentable sugars, maythen be fermented by any suitable method, to produce ethanol asindicated by step 116 of FIG. 1. For example, yeast, geneticallyengineered strains of E. coli, or other commercially available productsmay be used to convert the sugars to ethanol. Initially, the solublesugars may be converted to a more desirable sugar by enzymes.

Alternatively, the soluble sugars may be directed to a process forcarmelization of the soluble sugars, such as sucrose and glucose.Carmelization provides desirable color and flavor in bakery's goods,coffee, beverages, beer and peanuts. Specifically, the carmelizationprocess can produce useful compounds, such as furans likehydroxymethylfurfural (HMF) and hydroxyacetylfuran (HAF), furanones suchas hydroxydimethylfuranone (HDF), dihydroxydimethylfuranone (DDF) andmaltol from disaccharides and hydroxymaltol from monosaccharides.Hydroxymethylfurfural (HMF) is found in honey, juices, milk but also incigarettes. Thus, as well as producing a feedstock for the production ofethanol, the present invention may also provide a feedstock for theproduction of valuable food component, such as hydroxymethylfurfural.

Example I

1 gram of grass (a cellulose-containing material) was combined with 1gram of kaolinite (solid acid material). The grass was oven dried at 80°C. to a moisture content of 4% by mass. The materials were placed in ahardened 440C steel vial with 3 440C steel balls ½″ in diameter. Thevial was agitated at ambient temperature in a SPEX8000D mixer mill in0.5 hour increments with 0.5 hours allowed between each milling intervalfor cooling. It was found that there was no difference between millingfor 2 hours continuously and interval milling. The mixture was milledfor a total of 2 hours. Total solubilization was measured by extractingapproximately 0.1 g of the milled material with 60 mL of distilled waterand filtration through a 47 mm diameter Whatman Nuclepore® track etchedpolycarbonate membrane filter with a pore size of 0.220 μm. The residuewas dried in an 80° C. oven for 12 hours and then weighed. From thisvalue a total solubilization of 80±3% was determined. In comparison, 2grams of grass without any solid acid, milled under the same conditions,exhibited a solubilization of 22±3% by mass.

The present invention, in various embodiments, includes components,methods, processes, systems and/or apparatus substantially as depictedand described herein, including various embodiments, subcombinations,and subsets thereof. Those of skill in the art will understand how tomake and use the present invention after understanding the presentdisclosure. The present invention, in various embodiments, includesproviding devices and processes in the absence of items not depictedand/or described herein or in various embodiments hereof, including inthe absence of such items as may have been used in previous devices orprocesses, e.g., for improving performance, achieving ease and/orreducing cost of implementation.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of theinvention are grouped together in one or more embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the followingclaims are hereby incorporated into this Detailed Description, with eachclaim standing on its own as a separate preferred embodiment of theinvention.

Moreover, though the description of the invention has includeddescription of one or more embodiments and certain variations andmodifications, other variations and modifications are within the scopeof the invention, e.g., as may be within the skill and knowledge ofthose in the art, after understanding the present disclosure. It isintended to obtain rights which include alternative embodiments to theextent permitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges or steps to those claimed, whether or notsuch alternate, interchangeable and/or equivalent structures, functions,ranges or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

1. A composition comprised of a soluble fraction obtained fromsolid-acid hydrolysis of a cellulose containing material, saidcomposition comprising a polysaccharide oligomer content that comprisespolysaccharide oligomers having a general formula of (C6H10O5)_(n) wheren is no greater than
 2. 2. The composition of claim 1, wherein saidpolysaccharide oligomer content comprises at least 70 percentpolysaccharide oligmers having a general formula of (C6H10O5)_(n) wheren is no greater than
 2. 3. The composition of claim 1, wherein saidpolysaccharide oligomer content comprises at least 80 percentpolysaccharide oligmers having a general formula of (C6H10O5)_(n) wheren is no greater than
 2. 4. The composition of claim 1, wherein saidpolysaccharide oligomer content comprises at least 90 percentpolysaccharide oligmers having a general formula of (C6H10O5)_(n) wheren is no greater than
 2. 5. The composition of claim 1, wherein saidpolysaccharide oligomer content comprises at least 95 percentpolysaccharide oligmers having a general formula of (C6H10O5)_(n) wheren is no greater than
 2. 6. The composition of claim 1, wherein saidcomposition also comprises at least 3 of cellobiose, glucose, fructose,levoglucosan, levoglucosenone, furfural, and 5-hydroxymethylfurural. 7.The composition of claim 1, wherein said composition compriseslevoglucosenone and/or furfural.
 8. The composition of claim 1, whereinsaid composition comprises levoglucosenone.
 9. The composition of claim1, wherein said composition comprises furfural.
 10. A compositioncomprised of a soluble fraction obtained from agitating a cellulosecontaining material in the presence of a solid acid material, saidcomposition comprising levoglucosenone and/or furfural.
 11. Thecomposition of claim 10 further comprising at least one of cellobiose,glucose, fructose levoglucosan or 5-hydroxymethylfurural.
 12. Thecomposition of claim 10, wherein said composition comprisespolysaccharides having a general formula of (C6H10O5)n where n is nogreater than
 2. 13. The composition of claim 10 made by a processcomprising (a) contacting the cellulose-containing material with a solidacid material; and (b) agitating the cellulose-containing material andthe solid acid material for a time sufficient to produce a productcomprising soluble sugars, wherein agitating occurs at a temperature ofbetween about −5 to about 105 degrees Celsius and wherein saidcellulose-containing material and solid acid material have a combinedfree water content of 45% or less.